We had a customer using ACT! (we forgave them for that) who wanted data migrated to Dynamics CRM. Here is a generic overview of how it was done.
1. Backup the existing ACT! database into a .zip file
2. Download the ACT! Reader Utility
Run it and enable SQL read-only access
3. Use SQL Management Studio to connect to the ACT! database instance, default is "ACT7"
The database structure is very straight forward
4. Write some .NET code to import the data into SQL
Notes in ACT! are in RTF format, you'll need to convert them to plain text before importing into Dynamics CRM
Attachments are stored in the file system, you'll need to lookup the filename and find the correct physical location if you want to attach the file into Dynamics CRM
Only the subject line of emails are stored in ACT!
ACT! Reader Utility - http://kb.sagesoftwareonline.com/cgi-bin/sagesoftwareonline.cfg/php/enduser/fattach_get.php?p_sid=3ROImuPj&p_li=&p_accessibility=&p_redirect=&p_file_id=16370&p_tbl=9&p_id=22989&p_created=1240323461&p_olh=0
SQL Management Studio 2005 - http://www.microsoft.com/downloads/details.aspx?FamilyId=C243A5AE-4BD1-4E3D-94B8-5A0F62BF7796&displaylang=en
XrmLinq - http://www.xrmlinq.com